Kinetic Condensation and Evaporation of Metallic Iron and Implications for Metallic Iron Dust Formation

Details Kinetic Condensation and Evaporation of Metallic Iron and Implications for Metallic Iron Dust Formation Kinetic Condensation and Evaporation of Metallic Iron and Implications for Metallic Iron Dust Formation

Jul 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011apj...736...16t&link_type=abstract

The Astrophysical Journal, Volume 736, Issue 1, article id. 16 (2011).

Astronomy and Astrophysics

Astronomy

1

Astrochemistry, Meteorites, Meteors, Meteoroids, Methods: Laboratory, Protoplanetary Disks, Stars: Agb And Post-Agb

Scientific paper

Metallic iron is one of the most abundant condensing materials in systems of solar abundance. Because metallic iron is responsible for the continuum opacity of dust particles, it has a large contribution to the thermal structure of circumstellar environments and hence to dust evolution itself. In order to understand the formation processes of metallic iron in circumstellar environments, condensation and evaporation kinetics of metallic iron were studied experimentally. Metallic iron condenses at the maximum rate with the condensation coefficient (a parameter ranging from 0 to 1 to represent kinetic hindrance for surface reaction) of unity under high supersaturation conditions, and evaporates nearly ideally (evaporation coefficient of unity) in vacuum. On the other hand, evaporation of metallic iron takes place with more kinetic hindrance in the presence of metallic iron vapor. It is also found that metallic iron atoms nucleate heterogeneously on Al2O3. Metallic iron does not necessarily condense homogeneously in circumstellar environments, but might condense through heterogeneous nucleation on pre-existing dust. Metallic iron formation proceeds with little kinetic hindrance for highly unequilibrated conditions, but the effects of kinetic hindrance may appear for evaporation and condensation occurring near equilibrium with a timescale of months to years in protoplanetary disks.

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